The gripper supports for the discrete grippers of cooperating gripper systems for the turning drums of combination first printing and perfecting printing type sheet-fed rotary presses are generally not vertically adjustable. Gripper systems of this kind have been disclosed, for example, in U.S. Pat. Nos. 2,757,610 and 3,385,597. Their range of use is therefore limited since they cannot provide accurate processing of relatively thick kinds of paper stock nor of printing board.
It is also generally known, and it has been disclosed, for example, in U.S. Pat. No. 1,208,731 and DE-PS No. 812,431, that the supports for the grippers of oscillating systems and for gripper systems disposed on a rotating impression cylinder may be adapted for central or individual vertical adjustment. However, these gripper systems have nothing to do with a sheet turning drum for perfecting presses. Theoretically, it is possible for the adjustment described in the patent specifications mentioned and using a drawing wedge (U.S. Pat. No. 1,208,731) or an eccentric bushing (DE-PS No. 812,431) to be transferred to turning drums. However, because of the constructional and operational features of the two correlatively cooperating gripper systems of a turning drum, more particularly because of the considerations associated with substantial printing widths and the accompanying severe torsional deformation of the pivot shaft and very reduced free spaces for the gripper systems, which oscillate towards and away from one another, it has so far proved impossible for the known vertical adjustment facilities to be incorporated in and operate satisfactorily in the gripper systems of a turning drum.